Technical Field
The present disclosure relates to a voltage conversion circuit and an organic light-emitting display device having the voltage conversion circuit.
Description of the Related Art
Organic light-emitting display devices having recently attracted attention as display devices employ organic light-emitting diodes (OLED) that emit light by themselves, and thus have great advantages such as a high response speed, high emission efficiency, high luminance, and a large viewing angle.
In such organic light-emitting display devices, sub pixels including an organic light-emitting diode are arranged in a matrix and brightness of the sub pixels selected by a scan signal is controlled on the basis of gray scales of data.
Each sub pixel in such organic light-emitting display devices generally includes a driving transistor that drives the organic light-emitting diode, a switching transistor that transmits a data voltage to a gate node of the driving transistor, and a storage capacitor that functions to hold a constant voltage for one frame time.
The driving transistor of each sub pixel degrades with extension of a driving time and thus characteristics of the driving transistor such as a threshold voltage and mobility thereof may be varied. Since a degree of degradation may differ depending on the particular driving transistors, a characteristic deviation may occur between the driving transistors of the sub pixels.
The organic light-emitting diode of each sub pixel also degrades with extension of the driving time and thus characteristics such as a threshold voltage may be varied. Since the degree of degradation may differ depending on the organic light-emitting diodes, a characteristic deviation may occur between the organic light-emitting diodes of the sub pixels.
As described above, the characteristic deviation between the sub pixels may cause a luminance deviation between the sub pixels and may cause screen abnormality such as a screen afterimage or luminance unevenness in a display panel.
Therefore, techniques of compensating for the characteristic deviation between the sub pixels have been developed. In a compensation method of the techniques, when an organic light-emitting display device operates in a sensing mode, characteristics of the driving transistor or the organic light-emitting diode of each sub pixel are sensed to acquire sensed values (Vsen) and data to be supplied to the sub pixel is compensated for on the basis of the sensed values (Vsen).
An organic light-emitting display device may operate in a display mode for displaying an image and a sensing mode for compensating for a characteristic deviation between sub pixels. A base voltage (EVSS) supplied to a cathode (a second electrode) of the organic light-emitting diode of each sub pixel may differ depending on the modes.
As described above, since voltage sources corresponding to the modes should be provided for supplying different base voltages (EVSS) to the display panel, there are disadvantages that circuits are complicated and the number of components to be added also increases.